benchmarks won't build with cmake+make

[nyx191]

GNU/Linux platform:
GNU ld-2.35.1
cmake version 3.18.4
GNU Make 4.3
gfortran-9.3.0 || gfortran-10.2.0
g++-10.2.1 || g++-9.3.0 || clang++ version 11.0.0 || clang++ version 9.0.1
Command sequence:

$ cmake -D BUILD_TESTING=ON -D FORTRAN_BENCHMARKS=ON ..
$ make benchmark # Fails

The problem is:

/usr/bin/ld: CMakeFiles/benchmark-floop9.dir/floop9.cpp.o: in function F77Version(blitz::BenchmarkExt<int>&)':
floop9.cpp:(.text+0x19b5): undefined reference to floop9_f77'
/usr/bin/ld: floop9.cpp:(.text+0x19f9): undefined reference to `floop9_f77overhead'

Builds w/o -D FORTRAN_BENCHMARKS=ON